Pop up sprays only bubbling even with 70psi in the lines

Hello members, first post for me. I’m resurrecting the front yard sprinkler system that came with my house when I bought it here in Phoenix Arizona so I can add a 20’ x 20’ area of grass. The one zone for drip irrigation for my shrubs works fine. My problem is with the second zone for pop up sprays. It sounds crazy, but there are 9 rainbird four inch pop ups on this one zone. The valve is a Rainbird 100DVF. I replaced that with a new one, so diaphragm, bleeder and flow control are all working well. Tested valve both with electric power and manual. When valve is opened, the pop ups only bubble up water, they won’t stay up. I installed 9 new Orbit 4” pop ups with 15 foot adjustable nozzles. Most are open at only 90 or 180 degrees. Nothing but bubbling water. So I capped all 9 lines and tested for pressure. Entire system is sealed, no hidden underground leaks. At the hose spigot on the house near the valve box I get a read of 72 psi. Now with a closed system, I get a reading of 70 psi at any of the pop up head connections points. So I installed just one pop up head and it works great. Then I tried to add a second head and only get bubbling from the two connected heads. I tried one head alone in various connection points and one head alone works, but no more, not 2,3,4, etc. Orbits installation guide says a house with 70 psi can handle 10 pop ups. Why can’t I even get two to work properly? This problem is driving me crazy. The pipe layout in the front yard is all one inch pvc pipe. All water line valves are fully opened at the PVB backflow prevention unit (which has new internal parts) and the water feed line from the main. Entire area covered by these pop ups is less than 20’ x 20’. Even if I could get 4 or 5 to work with 15’ adjustable nozzles I’d be happy. Or cut back to 8’ adjustable nozzles. But I can’t get more than one head to stay up. Please help! And thank you in advance for your expertise.